This invention relates to vehicle exhaust systems, in particular to systems having unequal length exhaust pipes and to a muffler including unequal length internal inlet pipes for equalizing the length of connected pairs of pipes delivering exhaust gas flow to the muffler interior.
In automotive vehicles with longitudinally-mounted engines having exhaust systems with dual exhaust pipes leading to a single muffler, the dual exhaust pipes may have essentially equal lengths. Such systems tend to deliver to the muffler exhaust gas having similar sound wave and gas flow patterns, which generally results in a pleasant sound quality of the engine exhaust note.
On the other hand, transverse-mounted engines may have exhaust systems with dual exhaust pipes leading from opposite front and rear cylinder banks of the engine to a single muffler. In such systems the exhaust pipes may have a difference in length that is in excess of one meter. This difference yields sound wave additions and cancellations, causing the quality of the exhaust note to be substantially inferior to those systems that have nearly equal length geometries. The result is typically a xe2x80x9craspyxe2x80x9d quality to the exhaust note.
A further characteristic of high flow low back pressure exhaust systems is that, when the exhaust flow rates are low, the back pressure is reduced and the systems are subject to pulsations which interfere with equal internal distribution of recirculated exhaust gas (EGR) to the cylinders.
Accordingly, a system is desired which improves the sound quality of exhaust systems for vehicles with transversely-mounted engines and other systems with differing dual exhaust pipe lengths. Preferably, the system could also improve EGR distribution at low exhaust flow rates without causing excessive exhaust back pressure at high exhaust flow rates.
The present invention provides an active muffler and vehicle exhaust system, particularly for transverse engines but applicable to other vehicle engines. The system provides the benefits of equal or nearly length exhaust pipe systems of longitudinally-mounted engines to exhaust systems where unequal length exhaust pipes are utilized.
In accordance with the invention, a single exhaust muffler is provided with separate first and second internal inlet pipes which have lengths differing by a predetermined length dimension. The difference in lengths is made equal, or nearly equal, to the difference in the lengths of exhaust pipes extending from the associated engine exhaust outlets to the single exhaust muffler. The inlet pipes are connected so that the total lengths of the pairs of inlet pipes with their corresponding connected exhaust pipes provide total lengths of exhaust flow paths which are approximately equal for gas flow from both engine banks to the interior of the muffler.
An optional additional feature of the muffler is the provision of dual outlet flow paths for the exhaust gas. These include a restricted gas flow path which is always open and a low restriction flow path controlled by a back pressure valve which closes the passage at low exhaust gas flow rates. The exhaust gas back pressure is thus raised at low flows so that EGR distribution to the cylinders is improved. The valve is opened at higher exhaust flow rates so that back pressure in the muffler is reduced, allowing the passage of exhaust gas through a high flow low back pressure system. This provides for high performance output of the engine, undiminished by excessive back pressure in the manifold. The dual outlet paths may also provide a performance sound to the high flow exhaust note.